Pressure ulcers significantly affect quality of life and overall healthcare costs of wheelchair users with spinal cord injury (SCI). Current clinical practice includes using wheelchair power seat function (PSF) to attain specific seating angles, durations, or frequencies that have been shown to reduce seating interface pressure in wheelchair users. PSF includes tilt (a change of seat angle orientation while maintaining the seat-to-back angle) and recline (a change of the seat-to-back angle). However, at what angle and timing PSF usage provides adequate pressure relief for enhancing skin blood flow and soft tissue viability is not clear. The long-term goal of this study is to determine the optimal PSF usage pattern for enhancing soft tissue viability, which may then help further advance the clinical guidelines of PSF usage for preventing pressure ulcers. Specific aim 1 is to investigate the acute blood flow response to PSF usage at various settings of tilt and recline angles. PSF usage has been demonstrated to reduce seating interface pressure in wheelchair users. However, the impact of PSF usage on skin blood flow and soft tissue viability requires further clarification. Common clinical recommendations of tilt (15, 30, and 45 degrees) and recline (100 and 120 degrees) angles will be examined. Total skin blood flow of a reactive hyperemic response will be used to assess soft tissue viability (ischemia) in this study. Specific aim 2 is to examine the effects of PSF usage at various settings of duration and frequency on the reactive hyperemic response to prolonged sitting-induced loads. Common clinical recommendations of duration (30 or 60 seconds) and frequency (15 or 30 minutes) of PSF usage will be compared to determine a proper setting for enhancing soft tissue viability in wheelchair users. Time to recovery of a reactive hyperemic response will be used to assess the effectiveness of PSF settings for relieving weight-bearing tissues. This study will demonstrate the feasibility of using skin blood flow to evaluate the effectiveness of PSF usage in enhancing tissue viability. The PIs'method will provide insight into the mechanism of blood flow response to PSF usage settings. Results from this study will provide objective evidence to support the use of PSF for needed pathological populations.